Yes, there were a lot of Janes. The complete family was
1783 Elizabeth
1786 William
1788 Catherine
1791 Jane
1795 Jane
1796 James
1798 Ann
1799 Jane
1801 John
1803 Isabel
1805 Esther
Charles Joughin, their father, lost three daughters, one in 1788 and two in 1794.

Although the wife of Caesar Caine could have been 1799 Jane, your #1c, it seems perverse to make that connection as Charles and Ann’s family were in Andreas, whereas your #2 was from a family already in Peel, where Jane and Caesar were married. The household recorded in the 1851 census at Kirk Michael Street, Peel also makes better sense if visitor Jane Agnes Joughin was Mrs. Kaighin’s first cousin, rather than a much more distant relation.